The present invention relates to a pressure vessel having an improved external seal for use under conditions of high hydrostatic pressure.
Instrument pressure vessels presently designed for oceanographic research under conditions of high hydrostatic pressure typically employ O-ring seals. Such seals are conventionally "piston" type or "compression" type seals. Such vessels have been employed to reach the deepest reaches of the oceans, such as the Marianas Trench which is 36,000 feet deep, and are as a result subjected to external hydrostatic pressures on the order of 18,000 psi. Even exposure to lesser ocean depths may subject the pressure vessel to hydrostatic pressures of at least 10,000 psi. It is thus critical that the opening in the vessel which permits access to the interior be sufficiently protected against the high pressures encountered and the effect of the surrounding water at such pressures. For example, water can wick into the interior of the pressure vessel through the joint between adjacent parts of the vessel if such joints are not properly protected.
Further, it is desirable to protect the material of which the pressure vessel is formed against the corrosive effects of sea water, especially in view of the fact that pressure vessels containing oceanographic research instruments often are in contact with sea water for extended periods of time.
Various types of pressure vessel configurations are known in the art as described by U.S. Pat. Nos. 2,547,521; 3,381,842; and 3,410,442, albeit for use in withstanding high internal pressures. The vessels described in these patents are tubular in configuration and include an end cap seated in an end opening of the vessel. Both end caps which are threadedly engaged with the vessel and circumferential collars can be employed to seal the joint between the end cap and the vessel. Since such vessels are adapted to withstand high internal versus external pressures, the manner by which the openings in the vessels are sealed would be unacceptable in an environment in which elevated external hydrostatic pressures are confronted.
U.S. Pat. No. 4,252,244 similarly is directed to a vessel adapted to withstand internal pressures. The patent discloses the use of successive shrinkable wraps which overlie an inner liner to assist the liner to withstand internal pressures. Such wraps are covered by an outer end cap. Such a vessel is also unacceptable for use in an elevated external hydrostatic pressure environment due to the number of exposed joints present on the exterior surface of the vessel.
U.S. Pat. Nos. 3,344,912; 3,358,902; and 4,226,327 each disclose the use of heat-shrinkable plastic materials to seal end portions of containers (e.g., food containers) or to provide an outer covering for a package. Of course, such disclosures bear little relevance to the sealing of a pressure vessel adapted for use under conditions of elevated hydrostatic pressure.
It is also known to employ heat-shrinkable tubing to provide a protective covering for various types of materials which are in contact with sea water, and especially are used to protect fiber-optic cables which are employed by the U.S. Navy in a manner which constantly exposes the cables to the effects of sea water. It is further known to employ pressure vessels comprised of composite materials such as fiber-reinforced plastics in an attempt to avoid the deleterious effect of sea water upon the metallic materials conventionally employed.